L13 - Cell Cycle Flashcards
purpose of the cell cycle?
copy entire genome for :
growth
replacement of lost/damaged cells
maintain cell number
how do prokaryotes divide
binary fission
describe process of prokaryote division
- DNA is attached to membrane
- cell enlarges and DNA duplicates
- septum forms (___|___) in middle of cell with DNA either side
- cells separate
what is unusual about DNA replication and cytokinesis in prokaryotes
they occur at same time - so have to be coordinated
describe DNA replication in prokaryotes
- there is 1 origin of replication
- helicase catalyses DNA unwinding forming two replication forks at origin (bidirectional)
- DNA pol works around DNA until the bottom where two circular copies are formed
describe prokaryote cytokinesis
- FtsZ is a protein that forms a ring of protein around the middle of the inner surface of PM
- this ring contracts
- PM on each side becomes so close that they fuse
- two cells
do cytokinesis and DNA replication take the same amount of time? (in prokaryotes)
no, DNA replication takes longer
how is DNA rep and cytokinesis co ordinated in prokaryotes
cells undergo multifork replication to ensure at least 1 round of replication is completed before cytokinesis
what is multifork replication
DNA replication is initiated before previous is completed
what are the phases of the Eukaryotic cell cycle (in order)
- G1
- S
- G2
- mitosis
describe what happens in G1
growth phase
doubling of organelles, proteins, enzymes etc
what happens in S phase
DNA replication
why mustn’t the newly replicated sister chromatids be separated too soon? how are they kept together
would affect attachment of mitotic spindle
hoop of cohesin around the pair held together by kleisin
what happens in G2
preparation for mitosis
what 3 events mark the beginning of mitosis
- chromosome condensation
- nuclear envelope breakdown
- mitotic spindle formation
what is interphase
G1 S G2
what happens during prophase
- chromosome condensation - condensin circles DNA and compresses (C become visible)
- nuclear envelope breaks down
why must the nuclear envelope break down early on in mitosis
so the spindle has access to the chromosomes
what happens during metaphase
mitotic spindle formation
chromosomes line up on equator
what happens during anaphase
separation of sister chromatids - kleisin cleaved, cohesin ring opens up, spindle attaches and begins shortening
what happens during telophase
chromatids separated to either end of cell
describe the process of cytokinesis
- nuclear membrane begins to reform
- cytoplasm divided in two by contractile ring of actin &myosin 2 filaments
- membranes pinch from outside in into two cells in middle
cell cycle variations : explain how cell cycles vary time wise
- timing differs between species
2. timing differs due to part of body cell is from eg liver 1 year cycle
cell cycle variations : how do cell cycles differ in size
eg somatic cells all same size as they grow after division
embryonic cells divide without growing so cells get smaller with each division
cell cycle variations : how do cell cycles differ in nuclear envelope dynamics
multicellular - open mitosis - nuclear envelope breaks down because spindle is outside nucleus
unicellular - closed mitosis - NE doesn’t break down
what is anchorage dependence
cells must be attatched to a surface to be able to divide
what is density dependant inhibition
cells stop dividing when they contact eachother (eg fill up a flat surface)
how is cell cycle controlled
- cell cycle engine
- co ordination (replicated DNA must undergo mitosis before replicating again)
- checkpoints
also
anchorage dependence
density dependant inhibition
explain the position of Restriction point checkpoint and its function
end of G1 before S
decides whether to initiate new cycle
explain the position and function of G2 checkpoint
in G2, checks if S phase has been completed
explain the location and function of the spindle checkpoint
start of mitosis
ensures spindle is attached to each chromosome
explain location of DNA damage checkpoint and its function
throughout cell cycle
if damage detected, cycle paused and fixed
what can failure in the DNA damage checkpoint lead to
damaged DNA being replicated - mutation - cancer
what can failure in the Restriction point checkpoint lead to
uncontrolled initiation of cell cycles - tumours
what can failure in the spindle checkpoint lead to
failure to separate chromosomes equally - aneuploidy/downsyndrome
accumulation of what protein will trigger cytokinesis in prokaryotes
FtsZ
what proteins ensure sister chromatids aren’t separated to early during mitosis and how
cohesin forms a loop held shut by kleisin
what protein mediates the centromere
kinetochore
what drives the cell cycle
cyclin and cyclin dependant kinase (CDK)
what 3 things will halt cell cycle
- no nutrients
- damaged DNA
- chromosomes fail to attach to mitotic spindle
what is the cell cycle engine
the protein complex that drives the cell cycle
what happens to levels of CDK throughout the cell cycle
remains the same, its the activity that changes
what happens to levels of cyclins throughout the cell cycle
rise and fall
what phase does cyclin E drive and what is the name of the cyclin involved
G1 into S
G1/S CDK
what phase of the cycle does cyclin B drive and what is the name of the cyclin involved
G2 into mitosis (induces NE breakdown)
M CDK
